This invention relates to a capacitive pressure sensor, and more particularly, to an inexpensive glass capacitive pressure sensor.
Capacitive pressure sensors work on the principle that the plates of a parallel plate capacitor form two walls of an enclosure which bounds a volume whose pressure is some reference pressure. Changes in the ambient pressure in relation to the reference pressure cause a flexing of at least one of the capacitor plates. Such a flexing changes the spacing between the capacitor plates and thus the capacitance measured between them. Thus, measuring the capacitance provides a measure of the ambient pressure with respect to the reference pressure. One such capacitive pressure sensor was disclosed in a related application entitled "Method for Fabricating A Vacuum Pressure Transducer" Ser. No. 835,372, by Earl K. Davis et al and assigned to the assignee of the present application. To obtain a large and measurable capacitance change for a given change in pressure the capacitor plate must be flexible enough to deform appreciably as the pressure changes. This can occasion difficulties with over pressures or large pressure changes since such a flexible diaphragm is easily susceptible to damage from large deflections. Alternatively, the capacitor plates can be closely spaced so that any deflection of the diaphragm represents a large percentage change in the capacitor plate spacing. Close spacings of the capacitor plates requires that the plates themselves be very flat across their entire dimension. One capacitive pressure sensor is disclosed in U.S. Pat. No. 2,999,385. That sensor, however, requires, among other things, the complex shaping of two glass plates. The above referenced application provides a large measure of improvement over this previous pressure sensor, but still requires the polishing of expensive capacitor plates and further requires a two step sealing process.
Accordingly, in view of the deficiencies of the prior art, it is an object of this invention to provide a sensitive, inexpensive, glass pressure sensor.
It is a further object of this invention to provide a sealing glass and a method of sealing together in one operation a capacitive pressure sensor.